This invention relates in general to methods for evaluating the condition of a lubricating material, such as oil, in a vehicle engine. In particular, this invention relates to an improved method for estimating when such a lubricating material should be changed.
Virtually all types of engines (such as internal combustion, diesel, and the like) use one or more lubricating materials, such as oil, to provide lubrication between engaging mechanical components that slide or otherwise move relative to one another. The use of such lubricating materials reduces the amount of friction that occurs between these engaging and sliding components, thereby minimizing the generation of undesirable heat and wear. It is well known that the ability of most lubricating materials to perform this function degrades as a result of use. As a result, replacing old lubricating material with new lubricating material too infrequently can result in damage to the engine. However, it is also known that replacing the lubricating material too frequently is undesirably wasteful.
Many engine manufacturers simply recommend that the lubricating material in the engine be replaced at predetermined fixed intervals of either distance traveled by the vehicle or amount of time of usage of the engine. For example, some engine manufacturers recommend that the lubricating material in the engine be replaced after a fixed amount of distance of travel by the vehicle, such as 7,500 miles. In other instances, engine manufacturers recommend that the lubricating material in the engine be replaced after a fixed amount of time of engine operation, such as 200 hours for example. In both instances, it is known to generate an audible and/or visual alarm to alert an operator of a vehicle when either or both of these fixed intervals has been reached.
Although these fixed interval types of systems have functioned satisfactorily, the fixed intervals that are used therein merely represent estimates that are based upon predetermined assumptions of operation of the vehicle. Consequently, if the vehicle is operated differently from those predetermined assumptions, then the fixed interval types of systems can estimate replacement of the lubricating material at less than optimal occasions (both sooner and later) than is desirable in light of the actual operating conditions of the engine. For example, it is known that an engine experiences relatively harsh operating conditions when operated at relatively extreme speeds (such as when the vehicle is either idling or driven at racing speeds), while an engine experiences relatively mild operating conditions when operated at relatively moderate speeds (such as when the vehicle is driven at moderate speeds). Thus, if the vehicle is idling or driven at racing speeds for an extended period of time (more than that assumed by a fixed interval type of system), it would be desirable to replace the lubricating material sooner than the predetermined time interval of 200 hours of engine operation. Conversely, if the vehicle is driven at moderate speeds for an extended period of time (again, more than that assumed by a fixed interval type of system), it would be desirable to replace the lubricating material later than the predetermined distance interval of 7,500 miles.
Additionally, the assumed correlation between amount of distance of traveled by the vehicle and the condition of the lubricating material used in the engine is even more tenuous in the context of hybrid vehicles, which are becoming increasingly popular. In such hybrid vehicles, the actual amount of use of the engine can vary widely depending upon how the hybrid vehicle is operated. For example, when driven for relatively small distances and time durations, the hybrid vehicle may be propelled primarily or exclusively by a battery-driven motor. In those situations, the engine may not used much (or at all) in relation to the amount of distance of traveled by the vehicle. However, when driven for relatively large distances and time durations, the hybrid vehicle may not be propelled much (or at all) by the battery-driven motor. Thus, the engine may be used quite a bit in relation to the amount of distance of traveled by the vehicle.
To address some of the shortcomings of fixed interval types of systems, it is also known to replace the lubricating material when any one of a plurality of engine operating parameters is reached. Such engine operating parameters can include, for example, a predetermined amount of fuel in the oil or a predetermined amount of soot in the oil. Each of these engine operating parameters can be detected by a conventional sensor and fed to a controller. In response thereto, the controller can generate an audible and/or visual alarm to an operator of a vehicle when either one (or both) of these engine operating parameters has been reached. Unfortunately, known systems that are responsive to engine operating parameters such as this are typically also responsive to either one of the above-described fixed intervals and, therefore, still suffer from the same shortcomings as described above. Thus, it would be desirable to provide an improved method for estimating when a lubricating material should be changed in response to the amount of actual usage of the engine.